/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.library.dprofile;

import org.apache.commons.math3.util.Pair;
import org.apache.iotdb.library.util.Util;
import org.apache.iotdb.udf.api.UDTF;
import org.apache.iotdb.udf.api.access.Row;
import org.apache.iotdb.udf.api.access.RowIterator;
import org.apache.iotdb.udf.api.access.RowWindow;
import org.apache.iotdb.udf.api.collector.PointCollector;
import org.apache.iotdb.udf.api.customizer.config.UDTFConfigurations;
import org.apache.iotdb.udf.api.customizer.parameter.UDFParameterValidator;
import org.apache.iotdb.udf.api.customizer.parameter.UDFParameters;
import org.apache.iotdb.udf.api.customizer.strategy.SlidingSizeWindowAccessStrategy;
import org.apache.iotdb.udf.api.type.Type;
import org.eclipse.collections.impl.list.mutable.primitive.DoubleArrayList;
import org.eclipse.collections.impl.list.mutable.primitive.IntArrayList;

/**
 * The function is used to compute the period of a numeric time series.
 */
public class UDAFPeriod implements UDTF {
    @Override
    public void validate(UDFParameterValidator validator) throws Exception {
        validator
                .validateInputSeriesNumber(1)
                .validateInputSeriesDataType(0, Type.FLOAT, Type.DOUBLE, Type.INT32, Type.INT64);
    }

    @Override
    public void beforeStart(UDFParameters parameters, UDTFConfigurations configurations)
            throws Exception {
        configurations
                .setAccessStrategy(new SlidingSizeWindowAccessStrategy(Integer.MAX_VALUE))
                .setOutputDataType(Type.INT32);
    }

    @Override
    public void transform(RowWindow rowWindow, PointCollector collector) throws Exception {
        DoubleArrayList value = new DoubleArrayList();
        RowIterator iterator = rowWindow.getRowIterator();
        while (iterator.hasNextRow()) {
            Row row = iterator.next();
            double v = Util.getValueAsDouble(row);
            if (Double.isFinite(v)) {
                value.add(v);
            } else {
                value.add(value.getLast());
            }
        }
        double[] corr = autoCorrelation(value.toArray());
        int[] peeks = findPeeks(corr).toArray();
        int period = 0;
        if (peeks.length > 1) {
            int[] gap = Util.variation(peeks);
            period = (int) new IntArrayList(gap).median();
        }
        collector.putInt(0, period);
    }

    private IntArrayList findPeeks(double[] x) {
        int window = 100;
        IntArrayList peeks = new IntArrayList();
        peeks.add(0);
        double threshold = 0.5;
        for (int i = 1; i < Math.min(x.length - 1, window); i++) {
            if (x[i] > x[i - 1] && x[i] > x[i + 1] && x[i] > threshold) {
                window = i;
                break;
            }
        }
        for (int i = 0; i + window <= x.length; i++) {
            double v = x[i + window / 2];
            if (v > threshold) {
                Pair<Double, Integer> p = max(x, i, i + window);
                if (p.getSecond() == i + window / 2) {
                    peeks.add(p.getSecond());
                }
            }
        }
        return peeks;
    }

    private Pair<Double, Integer> max(double[] x, int startIndex, int endIndex) {
        double maxValue = -Double.MAX_VALUE;
        int maxIndex = -1;
        for (int i = startIndex; i < endIndex; i++) {
            if (x[i] > maxValue) {
                maxValue = x[i];
                maxIndex = i;
            }
        }
        return Pair.create(x[maxIndex], maxIndex);
    }

    private double[] autoCorrelation(double[] x) {
        double[] corr = new double[x.length];
        for (int i = 0; i < x.length; i++) {
            corr[i] = pearson(x, x.length - i);
        }
        return corr;
    }

    /**
     * auto correlation (pearson of subseries)
     */
    private double pearson(double[] x, int subLength) {
        double sum_x = 0;
        double sum_y = 0;
        double sum_xx = 0;
        double sum_yy = 0;
        double sum_xy = 0;
        int s1 = 0;
        int s2 = x.length - subLength;
        for (int i = 0; i < subLength; i++) {
            sum_x += x[s1 + i];
            sum_y += x[s2 + i];
            sum_xx += x[s1 + i] * x[s1 + i];
            sum_yy += x[s2 + i] * x[s2 + i];
            sum_xy += x[s1 + i] * x[s2 + i];
        }
        return (subLength * sum_xy - sum_x * sum_y)
                / Math.sqrt(subLength * sum_xx - sum_x * sum_x)
                / Math.sqrt(subLength * sum_yy - sum_y * sum_y);
    }
}
